Graphitic, porous carbons for catalysts with increased stability in the proton exchange membrane fuel cell

• Applicant: Professor Dr.-Ing. Bastian Etzold
• Subject Area: Technical Chemistry
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 284032131

The proton exchange membrane fuel cell (PEMFC) is believed to be of great importance for a successful usage of sustainable energy, because it enables the conversion of sustainably produced hydrogen into electricity. Challenges for this technology are mainly increasing activity and stability of the electrocatalyst. This key component usually consists of a catalyst support based on carbon materials on which the active metal (e.g. platinum) is dispersed. In the last years the activity of these catalysts could be considerably increased by optimizing the structure of the active component, for instance in the form of metal alloys like PtNi. The stability of the catalyst is mainly limited by the carbon support. Employing non-carbon support materials can mitigate some of the disadvantages carbon supports inherit, e.g. the low stability against oxidation. Yet these materials give rise to other drawbacks like a poor electrical conductivity. Recently an extraordinary stability was reported when employing porous hollow graphitic spheres as electrocatalyst support. Reason for the stability is seen in the combination of inner porosity, mesopores with size similar to the dispersed platinum particles and the graphitic structure of the carbon material. In contrast to the typically used carbon black containing outer porosity these novel supports seem to 'trap' the active metal inside the pores. This shows that the stability of carbon supports can be increased to a satisfying level. In this proposal the described findings shall be applied to develop new mesoporous, graphitic carbon supports with inner porosity for stable PEMFC catalysts. The development will base on Carbide Derived Carbons (CDC) that are obtained by the reactive extraction of carbides, while crucial parameters like pore structure and degree of graphitization can be adjusted by the choice of carbide precursor and extraction temperature. The resulting carbon is very pure and the material properties can be obtained with a high reproducibility. Preliminary work showed that mesoporous and graphitic carbons are obtained at extraction temperatures above 1200 °C, which shall be employed within the project to vary the degree of graphitization and pore sizes of CDC based carbon supports. Furthermore a method for the deposition of platinum on these supports shall be developed, which result in homogeneous dispersion of the metal within the pore system. After Subsequently, the platinum clusters will be sintered to the size of the pores to allow for 'trapping'. The resulting catalysts will be tested regarding their activity and stability for the Oxygen Reduction Reaction with half-cell measurements. Further insights will be obtained by characterization of the pristine and used electrocatalysts with IL-TEM. In external cooperation optimized materials resulting will be studied in single stack fuel cell experiments for their long-term stability under realistic conditions.

• DFG Programme: Research Grants